Resins obtainable by chlorination of polyolefins have excellent properties in dissolution thereof in organic solvents and, therefore, are now industrially produced and used in a variety of fields. In particular, resins having a high chlorine content are used as corrosion-proof coatings for outdoor constructions, while resins having a low chlorine content which can adhere to polyolefin articles are used in an ink for polyolefin films or in a primer for coating polyolefin moldings.
Polyolefines are generally insoluble in aromatic organic solvents such as toluene and xylene but become soluble in organic solvents when chlorine is introduced thereinto.
Various methods are known to chlorinate polyolefins. They may be roughly classified into a method in which a polyolefin is chlorinated in the form of a suspended liquid (see Japanese Patent Publication No. Showa 36(1961)-4745, for example), a method in which a polyolefin is chlorinated in the form of a solution (see Japanese Patent Application Laid-Open No. Showa 48(1973)-8856, for example), and a method in which a polyolefin is chlorinated in the form of a bulk (see Japanese Patent Application Laid-Open No. Showa 46(1971)-737, for example). The suspended liquid chlorination method is carried out in such a manner that a polyolefin in the form of fine particles is suspended in water and chlorine gas is blown into the resulting suspended liquid while irradiating ultraviolet rays or after addition of a radical generating agent. After termination of the chlorination, the chlorinated product is separated from water and dried. The solution chlorination method is performed by dissolving a polyolefin in a chlorine-containing organic solvent which is inert to chlorine, such as carbon tetrachloride, chloroform, methylene chloride or trichloroethane, for example. Chlorine gas is blown into the resulting solution to chlorinate the polyolefin while irradiating ultraviolet rays or after addition of a radical generating agent. The product is separated from the solvent to obtain a chlorinated polyolefin. A method is also known in which a hydrocarbon solvent is used (see Japanese Patent Application Laid-Open No. Heisei 03(1991)-197510, for example). The bulk chlorination method is performed in such a manner that a polyolefin in the form of powder is chlorinated by contact with chlorine gas using, for example, a fluidized bed system.
A chlorinated polypropylene, which can be dissolved in organic solvents and is easy to handle, is particularly utilized in various applications. Because of low solubility of polypropylene being the base polymer, it has been difficult to obtain a satisfactory solubility unless the chlorination degree is made high. In this case, however, a reduction of durability, etc. of the base polymer is inevitably caused.
As a problem of chlorinated polypropylenes, there may be mentioned a future trend for non-toluene type products. It is most likely that the use of aromatic solvents will be prohibited within three to five years from now. In the current industry, toluene is used in all products. Study and development are thus being made with a view toward the realization of non-toluene products after five years from now.